THE PLANT LOUSE, OR GREEN FLY. (Aphis.)
The Aphides are sometimes viviparous, and at other times oviparous, according to the season of the year. Those of the rose-tree have been particularly noticed, and of ten generations produced in one spring, summer, and autumn, the first nine were viviparous, and the last oviparous. The first nine generations consisted of females only; but in the tenth there were males. In this singular aberration from the common laws of nature this insect is a remarkable anomaly. They multiply at such an extraordinary rate—the whole ten generations within three months—that from a single Aphis ten thousand million millions may be produced in that short period, and it has been calculated that the progeny of a single Aphis during a single summer, supposing its multiplication to be subject to no check, might exceed in weight the entire human population of China.
The moss-rose, the hop, the vine, the apple-tree, the bean, the willow, and privet, are all particularly liable to be infested with this insect; the various species of which take their names according to the plants on which they are usually found. The red tumours, commonly called galls, which are seen on the surfaces of leaves, especially on those of the willow, varying from the size of a ladybird to that of a pigeon’s egg, are produced by Aphides, and contain thousands of small lice. From a pair of small tubes placed near the end of the body of these insects exudes a saccharine fluid, of which ants are very fond; and it is this fluid dropped upon the adjacent leaves, or the extravasated sap flowing from the wounds caused by the punctures of the insects, which is known under the name of honeydew.
After a mild spring, most of the species of Aphis become so numerous as to destroy all the young shoots of the plants on which they are found. No successful mode of destroying them has yet been discovered, but the best remedy against them is to wash the infested shoots with tobacco water or soap lees; and to repeat the operation when any Aphides are seen.
Order IV. Neuroptera.
These insects have four transparent wings, strongly and beautifully varied, so as to resemble net-work. The mouth has mandibles and maxillæ. The abdomen of the female has neither ovipositor nor sting.
